The present invention relates to a technique for inspecting cavity-like inner defects such as casting defects in casting parts. In particular, the present invention relates to a technique for inspecting an inner defect on the basis of spatial discrete data such as X-ray CT (Computed Tomography) data obtained by picking up an image of an object by using an X-ray CT apparatus.
In industrial products, a small cavity is generated inside a solid portion and becomes an inner defect that degrades the product performance in some cases. As a representative example of such an inner defect, there is a casting defect in a casting part. There is a possibility that the casting defect will exert a bad influence upon the strength or the like of the casting part. Therefore, a measure of decreasing occurrences of casting defects by adjusting the casting condition and controlling the occurrence position of casting defects by changing the shape of the runner of the die is adopted. Typically, in these measures, trial production and inspection are repeated at the stage of design and an optimum condition is searched for and determined. In the manufacturing field of casting parts, therefore, it becomes important to make it possible to inspect even a minimum casting defect with high precision.
As a technique for inspecting inner defects such as casting defects, there is a destructive inspection from old. In the destructive inspection, the inspection object is cut and its section is observed, or a cut piece obtained by cutting the object into dies is weighed. Such a destructive inspection requires labor and time, and the precision is not very high. In addition, it becomes impossible to conduct other tests such as a strength test on the object subjected to the destructive inspection, and the influence of inner defects upon the performance cannot be evaluated accurately.
On the other hand, nondestructive inspection of inner defects using an X-ray CT apparatus has become to be used in recent years. For example, in a system proposed in JP-A-7-12759, imaging of an inner section of a casting part is conducted using an X-ray CT apparatus and an inspection for inner defects is conducted. For example, in a system proposed in JP-A-2004-34144, a three-dimensional shape model of an object is generated from a plurality of sectional images picked up by an X-ray CT apparatus, and portions corresponding to inner defects in the three-dimensional shape model are colored to visually verify the inner defects. As for the inspection for casting defects, examples disclosed in JP-A-2004-12407 and JP-A-2003-530546 are also known.
The conventional techniques concerning the nondestructive inspection described above have merits that it is easy to visually grasp whether inner defects are present and positions of the inner defects. Especially in the method proposed in JP-A-2004-34144, three-dimensional distribution of inner defects can be grasped, resulting in a merit of reduced inspection labor and time.
In the method proposed in JP-A-2004-34144, however, it is necessary to generate a three-dimensional shape model of an object, resulting in a remained problem concerning the inspection precision and so on. For modeling an external shape of the object, a middle value between a CT value indicating a density of an inner defect portion (which is typically a density of air) and a CT value indicating a density of a solid portion is used as a threshold for modeling. Typically, in a sectional image obtained by an X-ray CT apparatus, however, a phenomenon that a boundary between an inner defect portion of a cavity structure such as a casting defect and a solid portion blurs, i.e., “blur” appears. In an inner defect of a minute cavity structure such as a casting defect in a casting part, therefore, a CT value of the defect portion (corresponding to a density of the defect portion) indicates a value shifted from an original CT value toward a CT value of a solid portion (corresponding to a density of the solid portion). In modeling using the threshold, such “blur” causes the size of the inner defect to become smaller than the actual size, or causes an inner defect having a size smaller than a definite size to become impossible in modeling itself, resulting in an insufficient inspection precision. If the threshold is made high so as to model even an inner defect having a small size, the volume of the inner defect differs according to the threshold, also resulting in lowered inspection precision. Furthermore, for modeling an inner defect with an accurate volume, it is necessary to make the threshold differ according to the size of the inner defect. As a result, the processing process of the inspection becomes complicated, and the inspection efficiency becomes lower.
In the context of the circumstances heretofore described, the present invention has been made.
A first object of the present invention is to provide an inner defect inspection method that makes it possible to conduct inner defect inspection using spatial discrete data such as X-ray CT data with higher precision and a higher efficiency.
A second object of the present invention is to provide an inner defect inspection apparatus that makes it possible to conduct inner defect inspection using spatial discrete data such as X-ray CT data with higher precision and a higher efficiency.
In order to achieve the first object in an inner defect inspection method for inspecting inner defects in an object on the basis of spatial discrete data which describe spatial shape and structure of the object by using spatial elements, the inner defect inspection method according to the present invention includes the steps of: extracting an inner defect from the spatial discrete data by using an inner defect extraction unit; collecting the elements included in a neighborhood range, which is set with a predetermined spread around the inner defect extracted by the inner defect extraction unit, as related elements by using a related element collection unit; and measuring feature quantities such as a size and a position of center of gravity of the inner defect on the basis of the related elements collected by the related element collection unit, by using a feature quantity measurement unit.
In order to achieve the first object in an inner defect inspection method for inspecting inner defects in an object on the basis of spatial discrete data which describe spatial shape and structure of the object by using spatial elements, the inner defect inspection method according to the present invention includes the steps of: measuring densities in the object on the basis of the spatial discrete data, finding density distribution, detecting an inner defect from the found density distribution, and setting a related region having a spread around a density measurement object region by using a region division setting unit; collecting the elements included in the related region set by the region division setting unit, from the spatial discrete data as related elements by using a related element collection unit; and measuring densities on the basis of the related elements collected by the related element collection unit, by using a density measurement unit.
In the inner defect inspection method according to the present invention, X-ray CT data is used as the spatial discrete data.
In order to achieve the second object, in an inner defect inspection apparatus for inspecting inner defects in an object on the basis of spatial discrete data which describe spatial shape and structure of the object by using spatial elements, the inner defect inspection apparatus according to the present invention includes: an inner defect extraction unit for extracting an inner defect from the spatial discrete data; a related element collection unit for collecting the elements included in a neighborhood range, which is set with a predetermined spread around the inner defect extracted by the inner defect extraction unit, as related elements; and a feature quantity measurement unit for measuring feature quantities such as a size and a position of center of gravity of the inner defect on the basis of the related elements collected by the related element collection unit.
In order to achieve the second object, in an inner defect inspection apparatus for inspecting inner defects in an object on the basis of spatial discrete data which describe spatial shape and structure of the object by using spatial elements, the inner defect inspection apparatus according to the present invention includes: a region division setting unit for measuring densities in the object on the basis of the spatial discrete data, finding density distribution, detecting an inner defect from the found density distribution, and setting a related region having a spread around a density measurement object region; a related element collection unit for collecting the elements included in the related region set by the region division setting unit, from the spatial discrete data as related elements; and a density measurement unit for measuring densities on the basis of the related elements collected by the related element collection unit.
In the inner defect inspection method according to the present invention, X-ray CT data is used as the spatial discrete data.
In accordance with the present invention, elements included in a neighborhood range, which is set with a predetermined spread around an inner defect are collected as related elements, and feature quantities of the inner defect are measured on the basis of the collected related elements. According to the present invention, therefore, it becomes possible to measure the feature quantities of the inner defects with high precision, resulting in raised inspection precision of the inner defects. It also becomes to conduct a series of processing automatically, resulting in highly efficient inspection.
In accordance with the present invention, densities in the object are measured on the basis of the spatial discrete data to find density distribution, and an inner defect is detected from the found density distribution. Elements included in a related region having a spread set around a density measurement object region are collected as related elements, and densities are measured on the basis of the related elements. According to the present invention, therefore, it is possible to efficiently detect inner defects such as microporosities formed by a large number of minute casting defects, each having a size of micrometer level, in a lump, resulting in raised inspection precision of the inner defects. It also becomes to conduct a series of processing automatically, resulting in highly efficient inspection.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.